Rules / Invader
Invader chess: rules and tactics for 15-second phases
Invader throws out the idea of one move per turn. In your phase, you have 15 seconds, and each of your pieces may move once. You can shift a whole army, or just one pawn, and then hand over. It plays more like a real-time strategy game than chess, and a phase passes very quickly.
The rules
- A phase lasts 15 seconds. Each piece can move once in a phase. You can press End phase to finish early.
- Castling uses up both the King and the Rook for that phase.
- Check is only judged when a phase ends. If your King is in check when your own phase ends, you lose immediately.
- During your phase you may leave your King in check, or even move it onto an attacked square. It only has to be safe by the end.
- If a King is actually captured, the side that took it wins.
- There's no en passant.
- The game is drawn after 50 phases per side with no capture or pawn move.
Checkmate isn't the end, a phase is
Because you can move several pieces, a check that looks deadly can often be answered. You might block with one piece and capture the attacker with another. So "mate" doesn't apply here. What counts is whether your King is attacked at the moment your phase ends.
That gives one simple priority: whatever else you're doing, spend the last few seconds confirming your King isn't in check. Running out of time with your King in check throws away the game, however far ahead you were.
The discovered attack wins on the spot
This is the tactic that defines the variant. Since each piece only moves once per phase, a piece that moves up to attack the King can't also capture it in the same phase. But a piece that has been waiting behind another one can.
In that position, Black isn't in check when White's phase begins. The knight is in the way. White moves it anywhere, the line opens, and the queen takes the King in the same phase. Black never gets a chance to answer.
So being out of check isn't the same as being safe. When your phase ends, look along every open line toward your King. If there's exactly one enemy piece between your King and an enemy queen, rook or bishop, you're in danger, even with no check on the board. Move your King off the line, or put one of your own pieces on it, before the clock runs out.
Practical tips
Keep your King's move in reserve
Each piece moves once, and that includes the King. If you move your King early in the phase and then open a line to it with another move, you can't run with the King again. Move other pieces first when you can.
Plan during your opponent's phase
You can see the board while your opponent moves, so use that time to choose your first moves. Fifteen seconds is enough for a handful of good moves if you've already decided on them, and for almost nothing if you haven't.
Each piece captures only once
A queen can't sweep through two pieces in one phase, so a pile of undefended pieces is less fragile than it looks. On the other hand, several different pieces can all capture in a single phase, so count how many of your pieces can be attacked at once.
Reading the screen
The clock shows the time left in the phase, and pieces that have already moved get an orange outline. Press End phase when you're done.
Next: Traps